1. Field of the Invention
The invention relates to a device for a headset to be connected to any telephone instrument in order for the user to choose whether to apply the handset or the headset merely by operating a switch on the amplifier. The amplifier must be designed so that the handset works in the usual manner when the switch is in its first position and it must be able to be adjusted so that the headset works exactly like the handset when the switch is in its second position, thus usually rendering further switch operating unnecessary.
2. Disclosure of the prior art
There are headset amplifiers on the marked designed so as to connect a certain type of headset to a certain type of telephone instrument and having controls which render the adaptation and adjustment of signal levels possible.
It is a well-known fact that various telephone systems apply a number of various telephone instruments where the impedance and the signal levels of both the microphone and the sound reproducer can vary from one type of instrument to another.
Two of the most commonly used systems are system Merlin (AT&T), which is extensively used on the American continent, and system DYAD (Siemens), which is used in Europe. There is a substantial difference between systems applying carbon microphones and systems applying electronic microphones, like for instance electret microphones or dynamic microphones. Even if the same type of microphone, for instance a carbon microphone, is applied by two systems, there are systems with different transmission levels. Furthermore, the wiring differs in the various telephone instruments and accordingly, even if the telephone instruments are provided with standard modular jacks for the connection of the handset to the telephone instrument, the polarity must be considered at the coupling. Consequently, previously only headset amplifiers designed for certain types of telephone instruments were produced.